Start-stop telegraph regenerators



Feb. 4, 1958 v. J. TERRY ETAL 2,822,422

` START-STOP TELEGRAPH REGENERATORS Filed Aug. 16, 1954 United States Patent START-'STOP'TELEGRAPH REGENERATORS Victor. John Terry, Donald Adams: Weir, and-NigelFred-I erick Fossey, London, England, assignors to Internationall Standard Electric Corporation, New York, N.

ppliatioll Allgllstl, 1954, Serial No. 450,011 Claimspriority, application Great Britain August 17, 1953 4 Claims. (CI. 1784-70) This, invention relates to electronic regenerative tele'- graph .repeatersfor start stop codes.

In such regenerators a time scale circuit of some kind is used.to` measureoit intervals at which the condition ofY an incoming lineisA examined and thisvcondition repeated intov the outgoingv line. synchronismY between the. station. from which the signals` are being received an-d the timescale circuit of the repeater isdependentY upon. the. time scale circuit being startedfrom aconvenienti z ero position upon the receipt of the startkv element ofasignal combination and being restored (to await another start element)` after the stop element has been examined. Astartelementfisusually a space. or no-current condition.

In receiving telegraph signals overl circuits liable to interference, for example. overradio circuits, al start:V element` mayA failY tov arrive and the time scale circuit'l will: be started up by a received spacing conditionA which: is` in:fact.one of the significant spacingl elements inv al signal combination. In: such acaselack of synchronisnrresultsanda number ofi characters may be printed incorrectly until'synchronismis regained.

The present invention` has for its object af means. for restoring synchronism quickly. To this end the? condition ofy the incoming line isv examined during theznominal stop element period, when the condition of the incoming line should be mark. If there is lack of synchronism there is an even chance of the condition being found to be space and if so found the time scale circuit after being restored to zero is not restarted until a subsequent mark to space transition occurs.

It` has been found that with this provision synchronism between the distant station and the repeater is quickly restored and the number of characters wrongly printed isminimised.

When the time scale circuit is restored to` zero the condition ofthe line outgoing from the` repeater` may' be: forcibly driven to mark. The. automatic insertion inthe outgoing signal of a stop element irrespective of the` condition of the incoming line is itself' known and isknown as forced stop insertion. It has been described and: claimed in. our earlier British Patents 692,411, 692,456 and 692,457, and in British Patent 653,867.

In the last mentioned patent there is alsodescribed means for suppressing the automatic application of the stop element to the outgoing line when a longspace signall is received on the incoming line. In the regenerator therein: described, a multivibrator circuit is arranged to apply conditioning impulses to any electronic switching circuit under control of a character timing circuit. If a spacing condition persists fromthe commencement of a start elementV for a period of 130` milliseconds,

f ICC 2a depend upon aI mark to space transition the case of lack of synchronism. Indeed, in theconditions described; the time scale circuit i'sV held away from the zero. condition during the receipt of.V a longspace;

According to one feature of the present invention an` electronic regenerativetelegraph repeater for startf-stop codes comprises an incoming-signal: line andl anoutgoing signal, line, a time scale circuit, means for starting said time scale circiut upon the initial appearance of a spacing condition on said incoming; signal line, meansk for examining-thev conditionv of said incoming signal lineat intervals under control. ofl said time scale circuit and for repeating each condition into said outgoing line, means. for restoring; the time scaley circuit to an initial position after an examination of the incoming signal-` line during the periodi when a stopl element' shouldv be present at theI end of acharacter and means, operative. wheny a spacing conditionis found to be present during such last mentioned examination;` for preventing the re-l start: of said time scale circuit until a. mark to space transition is received onsaid incomingsignal line.

The arrangements according to the present invention may becombined with. forced stop insertion, since this, assists in.- synchronism between the' regenerator and anyJ distant stationf to. which signals are transmitted from scribedy in: conjunction with the accompanying drawing which` shows the essential partsof a` regenerative repeaterv as described in` said British Patent` No. 692,411, modied tov carry out the` present invention, including alsof facilitiesfor forcedV stopinsertionand long. spacev trans.- mission.

In order to simplify.v the description and the accom panying draw-ing; as much asr possible the: drawing isf functional in; naturey each` symbol used standing for a device performing a particular function, thephysical nature. of they device andits manner of performing thev function being Well known;

Gate. circuits arewdenoted byy a circle the reference G- being applied to each; A numeral within* the circle' denotes thel numberof inputsr required to open the gate andI thus furnish an output. TwoA position switches are: denotedby the? letter 1F, 2F'&c.', the, different positionsv being denoted? by.- rectangles: within which different numeralsor letters appear. There are all to be consideredl as staticv electric switchesl andi may take the form of 'two' coldl cathode gaslled tubes interconnected so that when one isredi the otherislextinguished. When one of the' tubes is conducting it supplies a potential to` an output conductor. rllisVA output conductor is shown also in relation to the device tol whichI it supplies an input: and' denoted bya numeral and lower case reference letters. '[`l'1us.th'eswitch` 1FA` consistsl of ytwo interconnected tubes marked" ST and SZ' and they outputs from these respective tubes are marked lfst and. lfsz respectively and sup ply inputs-to gates G7.r and GI respectively. The switch IF supplies a. momentary output over the conductor shown" vertically from the top of ST leading to the input of -gate GS whenever the switch 1F- changesover from one'conditionY to another.

TC denotesV a counting circ-uit' which may take. the form of that described in l'British Patent No.. 692,411. and controls the application. of' potentials` to various other. circuits at' various. ti'rnes` in. the. time; scale offcounting,V

The counting circuit counts. pulses. from a5. kcJsz source;

elements. Hence a signal combination lasts for 140 milliseconds.

The line for incoming signals (not shown) is connected to a modulator in the same manner as in the last above mentioned patent. Pulses `from the. same kc./s. source as are counted by the counting chain TC, are applied to this modulator and appear on mark and space leads in the manner described in the last above mentioned patent. Conductors connected to these leads are denoted M and S respectively in the drawing.

For the stop condition (mark) switch 1F is initially in condition such that SZ is operative and 2F in condition such that 2F1 is operative. Switch 4F is initially in condition such that 4FM is operative. Switches 1F and 2F supply inputs lfsz and 211, respectively to a gate G1, another input to the gate being supplied by conductor S.

When a start element arrives pulses appear on conductor S and gate G1 opens. Switch 1F is operated to condition ST and supplies a potential of an input to gate G2 which opens to allow pulses from P to operate the counting chain TC. At the same time the momentary potential generated on the change over of 1F acts through gate G5 to reset the `counting chain to position O if it were not already in that position.

Pulses from lP are thereupon counted by TC which supplies potentials at given times. Conductors upon which these potentials appear are denoted by T followed by iigures which indicate the times in milliseconds at which these potentials appear.

The condition of the mark and space leads are examined at times l0, 30, 50, 70, 90 and 110 milliseconds by gates G7 and G8 and the conditions found are re peated to the outgoing lines MO, SO, by operating the two'condition switch 4F to condition M or condition S respectively. lf forced `stop insertion is not provided, the condition of the mark and space leads is also eX- amined at l30 milliseconds at gate G9 and the condition found repeated by operation of switch 4F.

At 140 milliseconds potential is applied to a gate G4 to operate and re-cycle switch 1F into its initial condition SZ. This renders ST inoperative and the supply of pulses from P to the counting chain ceases. At the same time the change over potential applied over gate GS resets the counting chain to initial position.

The switch 2F is operated to condition 1 whenever a mark appears on the incoming line. lf a spacing condition is detected at 130 milliseconds when the condition of the incoming line should be marking, switch 2F is operated to condition 0. This takes place over gate G3 which requires three inputs to open the gate, one 3f@ being derived from switch 3F when in condition 0. For the present it will be assumed that this input to gate G3 is present.

With switch 2F in condition 0, gate G1 cannot be opened because input 2f1 is locking and the time scale circuit cannot be restarted. When a marking condition subsequently appears on the incoming line, a pulse appears on conductor M and operates switch 2F into condition 1. At the `same time the output switch 4F is driven into condition M over gate G10 to repeat the marking condition to the outgoing line. On the subsequent appearance of a space on the incoming line, gate G1 is opened to re-start the time scale circuit.

If a spacing condition is present on the incoming line at time T130, the middle of what should be the stop element, this is an indication that synchronism between the transmitter from which signals are being received and the time scale circuit of the regenerative repeater Ihas been lost and the arrangement thus described assists in regaining synchronism quickly.

This is best made clear by means of an example. Suppose a combination SMSSSSM is sent, the rst element S being the start element and the last element M being the stop element and further suppose the start element is lost due to interference. The time scale circuit of the regenerative repeater will then be started by the lrst spacing element in the character i. e. 40 milliseconds late. The character read by the regenerator and retransmitted Will be SSSSMSX where the sixth element in the last-mentioned character S is the start element of the following character and the following element X may be mark or space. If, and only if, X is a space the invention assists in regaining synchronism. -In such case the regenerator stops and does not immediately restart. It' the following character be SSSSSSM, SSSSSMM, SSSSMMM, SSSMMMM or SSMMMMM this character will be the only character lost as the regenerator time scale circuit will start again in synchronism on the start element following the last mark. With other combina# tions `the time scale circuit will restart with the loss of one or more elements and the character will be mutilated. Again there will be an even chance whether the time scale circuit will be brought to a condition to await a mark to space transition, and synchronism will quicklyl be restored.

From the theoretical point of view it may seem that, if interference causes the stop element to appear as `a space, the invention can be damaging. `It must be noted, however, that if -this space persists over the period of the following start element the regenerator is likely to be thrown out of synchronism whether -with or without the arrangements of the invention. Without the invention the time scale circuit would in such circumstances start again too early, with the invention it starts again too late. Prolonged tests have shown that overall the invention results in a substantial improvement in that the number of characters wrongly printed when working under severe conditions `was reduced by 50% by the use of the invention.

It forced stop insertion is required, gate G10 is omitted, the examination of the incoming line by gates G7 and G8 at 130 milliseconds is omitted as shown and a gate G9 is provided over which switch4 4F is forcibly driven to mark at 140 milliseconds. Gate G9 a two input gate and receives an input pulse at time T130 and also receives an input 3f@ from switch 3F which is in the (l position.

It the facility of repeating a long vspace is alsoA to be provided the forcible insertion of mark at 130 milliseconds must be prevented during the receipt and retransmission of a long space and the bringing of the time scale circuit to rest ou a spacing condition being detected at 130 milliseconds must in those circumstances be pre-V vented. f

For these purposes switch 3F is provided. This switch is set into condition 1 at time T l millisecond in each cycle of the time scale circuit. The condition of the mark lead is examined at 30, 50, 70, and 110 milliseconds, i. e. at the middle point of each of the character elements and if a marking condition is detected at any one of those times switch 3F is driven into position 0. The driving of switch 2F into position 0 over gate G3` and the forcible insertion of a mark over gate G9 are dependent upon switch 3F being in condition 0.

It a long space is received switch 3F remains in condition 1 and switch 4F at ifs continues to repeat a spacing condition into the outgoing line. Switch 2F remains Ain position 1. The time scale circuit continuesJ to run. At 140 milliseconds switch 1F is driven into condition SZ via gate G4, the time scale circuit TC is restored to Zero position via gate GS and the spacing* condition on the incoming line drives switch 1F into con dition ST and restarts the time scale circuit from zerorestores to mark before milliseconds in a' cycle;

switch 3F is driven to 0 via gate G6, and at 130 milliseconds switch 4F is driven to condition M via gate G9. The circuit then awaits the arrival of a space in the ordinary way.

While the principles of the invention have been described above in connection with specific embodiments, and particular modifications thereof, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What we claim is:

l. An electronic regenerative telegraph repeater for start stop codes comprising an incoming signal line and an outgoing signal line, a time scale circuit, means for starting said time scale circuit upon the appearance of a start condition on said incoming signal line, means for examining the condition of said incoming signal line at intervals under control of said time scale circuit and for repeating each condition into said outgoing line, means for examining the incoming signal line during the period when a stop element should be present, means for restoring the time scale circuit to an initial position after the said last mentioned examination and means operative when a spacing condition is found on said last examination for preventing the restart of said time scale circuit until a mark to space transition is received on said incoming line.

2. An electronic regenerative telegraph repeater for start stop codes comprising an incoming signal line and an outgoing signal line, a time scale circuit, means for starting said time scale circuit upon the appearance of a start condition on said incoming signal line, means for examining the condition of said incoming line at intervals under control of said time scale circuit and for repeating each condition into said outgoing line, means for examining said incoming line at an interval during the nominal stop element, means for restoring the said time scale circuit into an initial position at an interval after the lapse of a period from said start condition equal to the length of a signal combination, means operative when a spacing condition is found at either of said lastmentioned intervals for restarting said time scale circuit into operation and means operative when a spacing condition is found on examination during the stop element and a marking condition is found in at least one of the preceding intervals for preventing the restart of said time scale circuit until a mark to space transition is received on said incoming line.

3. An electronic regenerative telegraph repeater as claimed in claim 2` in which means is provided for repeating the condition of the incoming line found on said last examination into said outgoing line.

4. An electronic regenerative telegraph repeater as claimed in claim 1 in which means is provided for sending a stop element into the outgoing line irrespective of the condition of the incoming line found on said last examination.

No references cited. 

